Polymer blends are mixtures of structurally different polymers or copolymers. Commercially important polymer blends are generally mechanical mixtures, which are made by melt blending the various polymers in an extruder or other suitable intensive mixer. Most polymer-blend pairs form immiscible two-phase structures. For miscible systems, properties close to additive, relative to the properties of the neat polymers, are typically obtained. For immiscible systems, however, the two-phase structure can result in toughness properties somewhat lower than would be predicted from simple additivity.
Multi-component polyester blends (e.g., polycarbonate/PET blends) tend to have poor thermal stability in the molten state. Part of this instability is due to the tendency of the blend components to undergo transesterification in the melt. This reaction can result in gas evolution, changes in melt viscosity, and if one of the polyesters is crystalline, a reduction in both the degree of crystallinity and the crystalline melting point.
Thus, there is a need in the art for polyester blends with improved toughness and thermal stability, and a higher degree of crystallinity and melting point. The present invention addresses this need as well as others that will become apparent from the following description and claims.